The Axon AX-100 guitar-to-midi converter uses a NiCd battery to power its CMOS backup memory. Eventually this battery will stop working and you will lose whatever setup you had stored and you will have a hard time replacing the battery. Here's how I replaced mine.
The original battery in my AX-100 was an Emmerich Z2A which is a 2.4V 65mAh NiCd battery. A Google search for "65mAh nicd" turned up some stuff in Poland and Germany and some other places, but nothing nearby. Try it yourself. Emmerich actually brags about producing non-standard batteries if you can believe it.
Update: It's now 2008. I clicked the "try it yourself" link above and behold, 65mAh NiCd batteries are now available for about $1+shipping on my continent, although they're 1.2V so it would still take two of them.
The original battery was soldered onto the main circuit board. This is bad design for a couple reasons: it is not convenient to replace, and if it leaks it may take out something on the board with it.
Since I couldn't find anything on the same continent in a 65mAh NiCd, I went with two 1.2V 110mAh NiCd cells from DigiKey. I've bought a lot of stuff from DigiKey and like them a lot. The two cells together make a 2.4V 110mAh battery.
The new cells are 1/3AA size. I couldn't find any battery holders for these, so I got an enclosed battery holder for 2 AA batteries at my local Radio Shack. I hacksawed out 2/3 of a AA battery worth of length, which was conveniently equal to the section between the two springs, and super glued the holder and cover back together after doing some sanding on the cut edges to make sure everything was straight and even and would fit back together nicely.
Unlike the AA batteries the holder was designed for, the new batteries do not have protruding buttons on the positive end to make contact with the holder's metal tabs, so I compensated by putting solder blobs on the holder's metal tabs. Now I have a very nice enclosed battery holder that shuts securely with a screw, and the batteries will be easily replaceable, and if anything leaks it should be contained.
The finished battery holder is really quite cute. Here it is with the cover removed:
Since my new 110mAh battery was greater capacity than the 65mAh original, I thought it would be appropriate to increase the charging current in approximate proportion, since that seems to be what NiCd batteries want. The battery charges through 2K2 resistor R21. I paralleled it with a 2K resistor. This more than doubles the current, to maybe 2mA, which is still pretty weak since a real trickle charge for a 110mAh NiCd would be about 5.5mA.
One end of the new 2K resistor is soldered to the left end of D21, the other to the positive battery lead:
I spliced some wires onto the battery holder's wires and covered the splices with heat shrink tubing for insulation and strength, and bound the wires together with heat shrink tubing for neatness. I snipped out the original battery, left the leads for soldering to, and soldered away.
Here it is with the daughtercard removed:
Because I soldered onto the original battery leads instead of using a removable connector, I used velcro to attach the battery holder inside the case so it can be easily removed with the main circuit board should the need arise, e.g., to replace power supply capacitors.
Yes, it was time consuming, but I'm happy with the results.
If you attempt this or any other modification to your equipment and mess it up, that is entirely your responsibility.
You have been duly noted: